Transparent soap (transparent solid detergents) is commercially valuable because of the high-grade impression by its transparency. Most of prior transparent solid detergents are made from higher fatty acid soap as the base and transparentizers such as glycerin, sucrose, sorbitol, etc. They are made by framing or milling, and in general, framed transparent soap has better transparency than milled soap. However, framing is not suitable for mass production because it takes about one month to obtain a stabilized shape. Moreover, it is known that higher fatty acid soap-based transparent soap made by these processes is not essentially different from ordinary opaque soap, that the former has the same drawbacks as the latter, e.g., irritation to skin, poor sudsing in hard water, and that it may opacify in use.
JPA55-25465 (i.e., Japanese patent application laid-open (tokkai) No. Sho 55-25465), discloses transparent solid detergents based on N-longchain acyl acidic amino acid salts, and JPA56-76499 discloses a method of manufacturing milled transparent solid detergents using N-long chain acylglutamic acid salts.
However, such transparent solid detergents disclosed in these patent documents have low storage stability, because the triethanolamine salt or the sodium salt is used as the N-longchain acylglutamic acid salt. Thus, the triethanolamine salt-based detergents become browned when stored at high temperatures, and the sodium salt-based detergents gradually crystalize during storage and finally opacify. Moreover, these transparent solid detergents still need further improvement on their usabilities such as sudsing, disintegration, adhesion, etc.
In view of the prior art described above, an object of this invention is to provide N-longchain acylglutamic acid salt-containing transparent solid detergents which have improved usabilities such as sudsing, disintegration, adhesion, etc., while maintaining storage stability in connection with their transparency and non-coloration, and which are less irritant to skin, hair, ocular mucosa, etc.